Some rioters, for instance, were photographed carrying zip ties, a plastic version of handcuffs, and one man was arrested allegedly carrying a pistol on the Capitol grounds.

“We’re not looking at this as a grand conspiracy, but we are interested in learning what people would do with things like zip ties,” said a law enforcement official, who, like others, spoke on the condition of anonymity to discuss the investigation…

Adding to the investigation’s urgency, Twitter on Friday noted that plans for future armed protests have begun circulating online, including a proposed second attack on the U.S. Capitol and assaults on state government buildings Jan. 17. Officials cautioned that there may be a variety of motives among those who broke into Congress, and they said that a key part of their investigation is determining whether any individuals or groups had planned in advance or were coordinating in the moment to commit violence against individual politicians. Others may simply have been caught up in the moment and committed rash, unplanned crimes, officials said.

Fresh in investigators’ minds is the group of men charged last year in Michigan — self-styled militia members — who are accused of plotting to kidnap that state’s governor and allegedly discussed storming the state Capitol and taking lawmakers hostage.